This invention relates to apparatus for the anaerobic digestion of organic matter and more particularly to a digester for controlling the process of the decomposition of organic matter to produce a useful gas and a liquid fertilizer.
The theory of anaerobic digestion and its application to produce methane are well known. Thus, many municipal sewage processing systems incorporate an anaerobic stage and use the gas produced during this time as a fuel for providing heat and operating stationary engines. The primary purpose of such systems, however, is not to produce the useful gas but rather to rapidly decontaminate and liquify the organic waste before dumping it into streams and landfills.
Such systems are impractical for farm usage where it is desired to efficiently produce a useful gas (approximately 70% methane and 30% carbon dioxide) and a high quality liquid fertilizer from manure and other forms of organic waste that have in the past either been wasted or have not been fully exploited.
In accordance with the present invention it is recognized that in the process of organic decay, i.e., digestion of organic waste, which results in the production of methane gas, different kinds of bacteria have to grow and do their work in sequence. First, various types of aerobic bacteria, i.e., bacteria that require oxygen, must form in the organic waste to convert oxygen from its free state into carbon dioxide and to otherwise decompose the material. Then, various types of anaerobic bacteria, i.e., bacteria that live in the absence of oxygen, must form and feed off the oxygen-freed, but still raw organic waste. As these bacteria become active, the products of the first provide food for the next until a food acceptable to the methane producing anaerobic bacteria is reached. Until the stage of methane production is reached the bacteria are relatively insensitive to changes in temperature. But, methane producing bacteria are very sensitive and must have favorable conditions in order to grow and multiply.
The digester of the present invention takes into account the activity and characteristics of the microbial action which takes place during the course of complete anaerobic digestion. Thus the digester is constructed to accommodate the natural behavior of the several forms of bacteria by providing three slurry chambers in tandem, each separated from the other by a passthrough tube, and a fourth chamber, located above the three slurry chambers, which serves to collect the gas produced. Of the three slurry chambers, only the second chamber is heated. Thus the non-heated first or input chamber receives the input load of the new waste material such as raw manure which is fed from a mix tank to the digester daily. This first chamber accomodates and separates the activity of the temperature insensitive bacteria and at the same time serves to insulate the second or incubation chamber which is heated to accomodate the temperature sensitive bacteria which produces methane. At the same time, advantage is taken of the heat lost from the heated second or incubation chamber to warm and thus stimulate digestion in the first chamber. This same warming is extended to the nonheated third or temporary storage chamber where biological activity slows down, yet some gas production is stimulated by heat. Then to further increase the efficiency of the operation, a required amount of digested manure which collects in the third chamber is recycled back to the mix tank. This not only serves to liquify and warm the new raw manure before it is fed into the first chamber, but, being saturated with bacteria, the digestive process begins immediately.
Accordingly, one of the subjects of the present invention is to provide an anaerobic digester that is practical for use on the farm or other animal raising areas for producing a fuel-type gas from organic waste materials.
Another object of the present invention is to provide a digester having separate chambers for accomodating the natural behavior of the several forms of bacterial action that take place in the course of the decomposition of raw organic matter to produce a useful gas and a liquid fertilizer.
Still another object of the present invention is to provide a cost-effective system for operating on organic waste matter to form a useful gas and a high quality liquid fertilizer.
Yet another object of the present invention is to provide an efficient anaerobic digester that is simply constructed, and easy to install and maintain on a farm.
With these and other objects and advantages in view, the invention consists of the construction, arrangement and combination of the various parts of the device, whereby the objects contemplated are obtained as hereinafter set forth, pointed out in the appended claims and illustrated in the accompanying drawings.